A. Field of the Invention
The invention relates generally to switching of messages in a packet/cell switching apparatus. The message switching is optimized for efficient switching of small messages, and is performed fully separated from the packet/cell switching.
B. Description of the Related Art
The input and output units of a general switching apparatus are connected respectively to the input and output links of a packet/cell switch element which resides inside the switching apparatus. Incoming packets/cells are switched from the input units to the output units via the packet/cell switch element in a packet and/or cell format. The typical packet format is a variable size frame with a typical size range from 32 to 10000 bytes, and the typical cell format is a fixed size frame with a typical size range from 32 to 80 bytes.
The input and output units of the switching apparatus may also require means for efficiently switching messages between the input and output units. Such messages are typically used for distributing information related to packet/cell input/output unit queuing status, packet/cell switching/scheduling credits, packet/cell flow control commands, and packet/cell control table state information. These messages are typically in the range of 2 to 16 bytes, which is smaller than the typical minimum packets and/or cell size. Furthermore, messages may be switched from input units to output units and vice versa, while packets/cells are typically only switched from input units to output units.
The packet/cell switch element is typically optimized for switching of packet and/or cells with a minimum size of 32 to 80 bytes, and therefore is inefficient for switching the smaller messages. One reason for this inefficiency is that a required switching header per packet/cell unit may be comparable in size to the message itself. The packet/cell switch element may also pad the size of the message up to a minimum packet/cell size, which also reduces the efficiency of the packet/cell switch element when used to switch small messages. It may also be a problem that when messages are switched across the packet/cell switch element together with packets/cells, the messages impact the packet/cell switching throughput and vice versa, and this results in non-deterministic switching performance for both messages and packets/cells.
One solution described in U.S. Patent Publication No. 2003/0103501 uses a separate ring element integrated inside a switch element to separate smaller messages from traffic data (packets/cells) which is switched across a crossbar. The ring element is constructed by successively connecting adjacent switch element links, forming a ring for passing the messages from an input link, successively through intermediate links, to the destination output link. The drawback of this approach is that although the messages and traffic data (packets/cells) use separate switching resources inside the switch element, they share the switch elements input and output links when passed to and from the switch element respectively. This structure means that the messages impact the switching of traffic data (packets/cells) and vice versa, which may result in non-deterministic switching performance for messages and traffic data (packets/cells).
Another solution described in patent U.S. Pat. No. 5,703,875 uses separate queuing resources inside a switch element to separate short control messages from longer data messages. Each input link has separate input queue resources to separate short and long messages, and all messages are switched using the same crossbar element. The drawback of this approach is that although the messages and traffic data (packets/cells) use separate queue resources inside the switch element, they share the switch elements input and output links when passed to and from the switch element respectively, and they also share the same crossbar element. This structure means that, the messages impact the switching of traffic data and vice versa, which may result in non-deterministic switching performance for messages and traffic data (packets/cells).